Progress in semiconductor technology has led to increased component density both in the integrated circuit chips themselves and in the packaging of the chips in assemblies of several chips known in the art by the term modules. The modules contain a group of interwired chips mounted in a housing assembly that facilitates attachment and connection to external wiring and dissipation of heat. While at the increased density, the individual chips involve very low currents, at the present state of the art the number of devices per chip may approach hundreds of thousands and the number of chips per module may approach a quantity of the order of a hundred, so that heat transfer has now become a most serious consideration.
One type of module package heretofore in the art transfers heat produced in the chip to the housing from the back of the chip through a viscous but conformal material, such as: a liquid metal as shown in U.S. Pat. No. 4,323,914; an oil filled porous layer as shown in U.S. Pat. No. 4,823,863; a thermal grease as shown in U.S. Pat. No. 4,567,505; and a thermal grease with a conformal foil as shown in IBM Technical Disclosure Bulletins Vol. 21, No. 1, June 1978, page 185 and Vol. 21, No. 4, September 1978, page 1473.
Another type of module package heretofore in the art employs an intermediate wafer of silicon on which is disposed some distribution wiring supported by a center post to provide thermal expansion movement and to which the chip contacts are bonded. One such module relies on a special material, AlN, as part of the package, shown in "Ultra Reliable HWSI With Aluminum Nitride Packaging" by J. K. Hagge in Electronic Packaging and Production, Sept. 1979, page 1271. Another such module shown in U.S. Pat. No. 3,999,105 employs liquid encapsulation.
The use of the center post supported intermediate wafer, of the same or thermal expansion matched material such as monocrystalline silicon, as density increases and dimensions decrease, may involve unpredictability and somewhat extensive movement since all heat may not be uniformly generated. In such a situation, fractures could appear in the intermediate wafer after only a few thermal cycles.